Many conventional earthmoving and construction vehicles utilize self-laying endless metallic track chain assemblies for supporting and propelling the vehicle. The segmented track chain is positively driven by a rear mounted sprocket wheel and guided by a front mounted idler wheel. Some type of subframe, pivotally secured to the vehicle main frame, supports a plurality of track guide rollers and the idler wheel. An idler recoil mechanism is normally incorporated into the subframe behind the idler wheel to provide a relief, or track recoil, function. The recoil mechanism normally utilizes a large steel coil spring which is held in a compressed state within the subframe. When debris, such as rocks or tree limbs, becomes lodged between the track and the idler wheel, or between the sprocket and the track, the idler wheel can retract rearwardly against the force of the compressed steel spring. The force, stored in the compressed spring, returns the idler wheel and track assembly back to their normal operating positions when the debris has passed out of the track assembly.
Conventional earthmoving vehicles, with endless steel track assemblies, are limited to relative low speed operation. Additionally, such vehicles are prohibited from traveling over or upon certain roadways because of the possible damage to the road surfaces by the steel tracks. Recent utilization of frictionally driven endless elastomeric track belts to replace the steel track assemblies has solved the problems of low speed operation and damage to road surfaces. However, conventional recoil and tensioning mechanisms are not satisfactory for the vehicles having frictionally driven endless elastomeric track belts.
A typical track idler recoil assembly for an endless steel track assembly of a track-type vehicle and the method for installation and removal of a recoil spring, is disclosed in U.S. Pat. No. 3,980,351 issued on Sept. 14, 1976 to Bobby J. Orr, et al. This assembly utilizes a large steel coiled compression-type recoil spring which is compressible between a spring housing and an hydraulic ram. The coil spring is maintained in its compressed state by a retaining member and a pushrod and the hydraulic ram connects the track idler to the compressed spring.
Another type of idler recoil and track adjuster spring retention arrangement, and the method of assembly and disassembly thereof, is disclosed in U.S. Pat. No. 3,920,286 issued on Nov. 18, 1975 to Francis D. Bell. This construction also uses a steel coil compression spring to provide idler recoil and use a threaded member to hold the spring in its compressed state. Both this patent and the above noted patent provide idler preloading and recoil operation using precompressed steel coil springs, which would appear to function satisfactorily for the track-type vehicles illustrated. However, both constructions are heavy and bulky, and require special methods of assembly and disassembly.
Another type of track idler recoil mechanism is described in U.S. Pat. No. 3,912,335 issued on Oct. 14, 1975 to George A. Fisher. This mechanism uses a combination of hydraulic and gas cylinders to replace the steel coil springs used in the previously noted patents. This construction is quite complicated and requires a considerable number of seals and closely machined mating piece parts.
The present invention is directed to overcoming one or more of the problems as set forth above.